Police in Uganda's capital have arrested Kizza Besigye, the main opposition candidate who challenged President Yoweri Museveni in Thursday's elections.
VOA spoke to an attorney for Besigye, who says the candidate was arrested early Thursday evening in the Nguru district of the capital, Kampala.
The attorney, Hajjat Lukwago Shifrah, says the candidate had discovered evidence of a vote rigging attempt.
Earlier, Uganda's electoral commission extended voting hours in some areas after many polling stations opened late.
Angry voters tear gassed
Police in Kampala fired tear gas at voters angered by problems at a polling station, one of many reported around Thursday.
Journalist Lizabeth Paulat, reporting for VOA, says officers fired the tear gas after people approached police lines, complaining they were unable to vote and that ballot boxes had been removed from the polling station before the end of voting hours.
Paulat reports that the incident at Gbagba Road junction ended after police withdrew and crowds dispersed.
Earlier, the Ugandan electoral commission said in a statement that "polling has started on time in various parts of the country" but noted delays in parts of the capital and in Wakiso District. The statement said the commission expresses its regrets for the late delivery of polling materials to those locations.
More than 15 million Ugandans are registered to vote in the elections for president, parliament and local government seats.
President Yoweri Museveni, in power for the past 30 years, faces a challenge from seven opponents, most prominently opposition leader Kizza Besigye, who has lost to him three times in the past.
Makerere University education student Ivan Ssebuliba said "If this is happening in Kampala, so close to the Electoral Commission, what is going on in the villages?"
Incomplete registers
Voters who had arrived early were forced to stand and wait in long lines in the heat, leaving them frustrated and irritable. But the electoral commission has assured voters that all who are in line by 4pm will be allowed to cast their ballots.
One man told VOA's Jill Craig "We shall vote tomorrow I think."
Some polling stations still remained closed as long as four hours after voting was scheduled to start, causing a confrontation between would-be voters and heavily-armored military police in the suburb of Kyabando Erisa.
At another polling station near the Electoral Commission, a polling observer - Simon Katum - said around 200 voters were left off the official register.
Election Day in Uganda
Social media blocked
Still others were upset by what seemed to be a block on social media. Kampala residents around the city have complained Thursday of difficulties accessing Twitter, Facebook, and Instagram.
The chairman of the Commonwealth Observer Group, former Nigerian President Olusegun Obasanjo, on Thursday asked participants in the election to "respect the franchise and refrain from acts of violence and intimidation." He said the observer group has been examining the whole election process, to determine whether it is compliant with Ugandan laws as well as international rules and standards.
He said, "We are all men and women of integrity and I do not believe any of us would want to sacrifice his or her integrity on the altar of unnecessary convenience."
Jill Craig and Lizabeth Paulat contributed to this report.
VOA's Lizabeth Paulat contributed to this report